DECLARATION 2 PUBLICATIONS
2.4 PRELIMINARY PROTOTYPE
2.4.2 Prototype testing
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2.4.1.3 Safety specification: general safety measures
The Touch Hand 3 is to be used indoor, in a dry, dirt-free and stable place. The amputee / user is to read the operator manual or get instruction and advise from the developers, before attempting to use it.
The user is to perform a pre-inspection on the device to validate performance, and to prevent malfunctions. In the event that any part of the Touch Hand 3 seems to be damaged, the amputee should cease to use it and get it repaired as soon as possible.
The Touch Hand 3 should go for maintenance on a yearly basis and prevent malfunction. The hand contains fuses to protect from overloading providing current protection of the circuits.
The hand is waterproof to an extent using silicone sealant to protect the electronics. It has mechanical stops, for example in the fingers, to control to range of motion as well as limit switches built into the motors.
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Figure 2-11. Posterior muscles of the forearm.
The prototype test setup can be seen in Figure 2-12 below. The two Arduino UNO boards are connected together, one receives the signals from the EMG’s, decodes them and sends them to the motor board which drives the prosthetic hand.
Figure 2-12. Prototype test setup.
Figure 2-13 shows the hand being tested by Mr. Andrew Mangezi. The figure also shows the position of the EMG’s on the forearm picking up the signal which could be decoded and sent to drive the prosthetic hand.
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Figure 2-13. Testing: Video analysis of touch hand 3 prototype.
For the case of our test subject, Darren, he was amputated just below the elbow and still had some of the radius and ulnar bones remaining in his forearm so that his socket could be connected just below his elbow. The EMG’s were connected then to the remaining muscles in his upper arm and these were used to control the hand. Figure 2-14 shows the amputee without his socket on, with EMG’s connected to his stump testing the prosthetic hand before it is fitted to the socket specially designed for him. This prototype used a standard connector found on all prosthetics to connect to the amputee’s socket.
Figure 2-14. Testing the prototype without attachment.
Figure 2-15 shows the socket and prototype hand being fitted to the amputees stump.
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Figure 2-15. Attaching the prototype to the amputees stump.
Figure 2-16 shows the attached prototype hand and the amputee learning to operate it.
Figure 2-16. The prototype attached.
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Figure 2-17 is of the amputee trying to pick up a chalk duster, the amputee is learning to grasp objects using the prototype hand.
Figure 2-17. Setup to pick up a chalk duster.
Figure 2-18 shows the amputee grasping the chalk duster.
Figure 2-18. Grasping a chalk duster.
Figure 2-19 shows the chalk duster being raised off the table in the grasp of the middle finger of the prosthetic hand.
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Figure 2-19. Picking up the chalk duster.
Figure 2-20 shows the amputee holding the chalk duster. The chalk duster is now firmly in the grip and control of the amputee.
Figure 2-20. Holding the chalk duster.
Figure 2-21 shows the amputee moving the chalk duster. This is taking quite a bit of skill by the amputee.
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Figure 2-21. Moving the chalk duster.
Figure 2-22 shows a different grip the amputee is using, known as a cylindrical grip to try to position the chalk duster on a plastic container. This is an easier grip and two fingers, index and middle are used to wrap around the chalk duster giving more grip strength. This shows the hand is working well in positioning these small objects.
Figure 2-22. Grasping the chalk duster between index and thumb.
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Figure 2-23 shows the amputee preparing to position the chalk duster on the plastic container.
This was carried out successfully.
Figure 2-23. Placing the chalk duster on a plastic container.
Figure 2-24 shows the amputee positioning the chalk duster to balance it on a small cylinder.
This required more fine motor skill than positioning the chalk duster on the plastic container and was a good test showing the capabilities of the prototype hand.
Figure 2-24. Manoeuvring the chalk duster to place on small cylinder.
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Figure 2-25 shows the amputee balancing the chalk duster on the small cylinder. This was carried out successfully.
Figure 2-25. Balancing a chalk duster on top of a small cylinder.
From the brief initial testing it was observed that the prototype design performed fairly well and some basic and slightly complex objects could be grasped and manipulated using the hand, the fingers could close around the objects and provided a fair amount of grip. Some fairly complex gripping and manipulation was carried out in the positioning of a chalk duster on top of a plastic cylinder. Problems with the design could be seen in the electronic system being slow to respond although with a bit of practice the amputee was able to get things working properly, understanding the way the EMG system operates and flexing his remaining muscles in the stump appropriately took a bit of practice.
From a mechanical point of view the problems with the prototype were its inherent bulkiness, fingers although actuating well did not close properly, weight was also a factor, the hand was quite heavy and its design had much to be improved on. Objects slipped easily from the hands grip. In order to solve this problem it was decided that further design needed to be done and possibly a glove employed which required a redesign of the fingers on the hand, making them narrow enough to fit into a glove. The hand also needed to be more lightweight and modular to allow for ease of assembly and repair. The weight needed to be reduced and the electronics needed to be incorporated into the hand.